JPH09174617A - Mold for molding substrate of optical recording medium and molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an optical disc substrate which has no sink mark in inside peripheral thick part and less double refraction when a thin optical disk substrate where the plate thickness of the inside peripheral part is larger than that of an information recording area, by an injection molding method. SOLUTION: A mold 1 is composed of a fixed die la and a moving die 1b, a recess 31 is formed on the compressed surface of the moving die 1b so that the substrate of an optical recording medium where the plate thickness of the inside perimeter is larger than that of an information recording area and the plate thickness of the information recording area is constant may be molded from a resin material. Within the moving die 1b, there are a piston 8 and cylinder 9 which compress only a resin material part forming the inside perimeter from the information recording area of the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold used for molding a thin optical disk substrate by an injection molding method, and more particularly to a metal mold for injection molding which does not cause sink marks on an optical disk substrate which is a molded product. The present invention relates to a mold and an optical disk substrate molding machine including the same.

[0002]

2. Description of the Related Art With the spread of personal computers in recent years, the amount of information handled by individuals has increased dramatically.
Recently, there has been an increasing number of applications in which various types of information such as documents, voices, and images are collectively handled by using a personal computer, and at the same time, a large capacity of external memory is required. As the external memory, an optical disk is excellent in terms of price, portability, and durability, and in particular, there is an increasing demand for large capacity of the optical disk. As one of methods for increasing the recording density of an optical disk, there is known a method of increasing the numerical aperture (NA) of the objective lens of the optical disk drive and decreasing the spot of laser light. However, when the method of increasing the NA is used, the amount of aberration due to the tilt of the optical disc increases, and the converged state of the light spot deteriorates. Therefore, there is a disadvantage that the allowable value of the tilt angle (warp angle) of the optical disc becomes small. It is generally known that the amount of aberration is proportional to the cube of the NA of the objective lens and the thickness of the substrate. As a means for preventing the above-mentioned defects, the thickness of the optical disc is reduced and it is caused by the inclination of the optical disc. A method of reducing the influence of the aberration that occurs is conceivable. However, depending on the resin, when trying to mold a thin substrate, the resin must pass through a very narrow gap in the mold, so high shear stress is required, and there is the problem that the resulting molded product has increased waviness and birefringence. It occurs newly.

As a method for solving the above-mentioned problem, Japanese Patent Laid-Open No. Hei 5
In JP-A-307769, by making the gap near the resin inlet of the mold wider than the distance from the resin inlet, the plate thickness of the inner peripheral portion of the molded optical disc substrate is smaller than that of the information recording region. Disclosed is a mold that can be made thicker and the thickness of the information recording area can be made constant, and a molding method using the same. According to this method, the outer peripheral portion of the disk substrate is forced by the thick inner peripheral portion to suppress the waviness of the substrate, and further, during molding, the shear stress received when the resin flows in the inner peripheral portion of the disk substrate. Has an effect of decreasing the birefringence and decreasing the birefringence. FIG. 2 shows an example of the structure of a mold part of a conventional substrate manufacturing apparatus for carrying out this method. The mold 11 includes a fixed mold 11a and a movable mold 11b.
The stamper 3 for manufacturing the optical disk substrate is mounted on the fixed mold 11a.
At the center of the compression surface of the movable mold 11b, a recess 34 is formed so that the clearance near the resin inlet (spruce portion) 26 is wider than the clearance on the outer peripheral side of the mold. When injection molding,
The movable mold 11b is clamped to the fixed mold 11a, and then the resin heated and melted in the gap between these molds is injected from the nozzle 5 provided on the central axis of the fixed mold 11a.

[0004]

However, when an optical disk substrate whose plate thickness on the inner peripheral side of the information recording area is thicker than the information recording area is formed using the mold having the above structure, the molten resin solidifies. At this time, sink marks are likely to occur in the thick wall portion on the inner circumference. Particularly, as the plate thickness difference between the inner peripheral thick portion and the information recording area increases, sink marks are more likely to occur in the inner thick portion. This sink mark defect is a phenomenon in which the final solidified portion of the molten resin becomes a concave shrinkage mark on the surface, which is one of molding defects. For this reason, the appearance of the molded optical disc is impaired. In the thick portion on the inner circumference of the substrate, the solidification of the molten resin is slower than in the thin portion of the information recording area, and especially in the thick portion and the portion where the thickness on the outer side in the radial direction gradually decreases, this solidification rate is uneven. Sink defects are likely to occur depending on the nature.

It is considered that the sink mark defect can be prevented by changing the molding conditions such as increasing the injection holding pressure, prolonging the injection holding pressure time, and lowering the mold temperature or the resin temperature. However, if the molding conditions are changed as described above, the resin tends to be oriented during molding, leading to an increase in birefringence of the disk substrate. For example, if the injection holding pressure is increased or the injection holding time is lengthened, the shear stress applied to the resin at the time of molding increases and the birefringence of the molded disk substrate increases. In particular, the birefringence of the information recording area on the inner peripheral side of the disk substrate is easily affected by the injection holding pressure and the injection holding pressure time. Further, if the mold temperature or the resin temperature is lowered, the fluidity of the resin at the time of molding is lowered and the shear stress at the time of resin filling is increased, so that the birefringence of the molded disk substrate increases. Such an increase in birefringence lowers the C / N ratio and causes an error in the reproduced signal in the optical disc in which information is recorded / reproduced by the laser beam.
Therefore, with the method of adjusting the molding conditions, it is extremely difficult to prevent the occurrence of sink defects in the thick inner peripheral portion while keeping the birefringence small.

Therefore, an object of the present invention is to eject a substrate for a thin optical recording medium in which the thickness of the inner peripheral portion of the information recording area is thicker than that of the information recording area and the thickness of the information recording area is constant. A mold capable of molding a substrate for an optical recording medium having a small birefringence without a sink mark defect in the thick inner peripheral portion of the molded optical recording medium when manufactured by a molding method, and molding using the same To provide a machine.

[0007]

According to the present invention, it is composed of a fixed mold and a movable mold, and the plate thickness on the inner peripheral side of the information recording region is thicker than the plate thickness of the information recording region and In a mold for injection molding a substrate of an optical recording medium having a constant plate thickness from a resin material, a resin forming an inner peripheral side of the information recording area of the substrate in the fixed mold or the movable mold. A mold for molding a substrate of an optical recording medium is provided, which is provided with a means for compressing only a material portion.

Since the mold of the present invention is provided with a mechanism for compressing only the resin portion forming the inner peripheral thick portion outside the information recording area of the optical recording medium, a sink defect occurs in the inner peripheral thick portion. Can be prevented. Therefore, injection holding pressure, injection holding time,
Molding conditions such as mold temperature and resin temperature are not limited to sink marks and can be set in a wide range. As a result, it is possible to obtain a substrate for an optical recording medium such as an optical disk which has a small birefringence of the substrate and has no sink mark on the thick inner peripheral portion.

Means for compressing only the resin material portion forming the inner peripheral side of the information recording area of the substrate is a piston and cylinder mechanism, and the fixed metal for contacting the compression surface of the piston with the resin material portion. It is preferable to form a part of the compression surface of the mold or the movable mold.

According to the present invention, there is provided a molding machine including the mold of the present invention.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a specific example of the injection molding die of the present invention. Mold 1 is fixed mold 1
It is configured by coaxially combining a and the movable mold 1b. A sprue bush 22 is inserted into the fixed mold 1a at its central axis position, and a fixed sleeve 23 and an inner peripheral stamper retainer 4 are coaxially inserted toward the outer side in the radial direction. A gas blowing passage (not shown) is formed between the fixed sleeve 23 and the inner peripheral stamper retainer 4, and the gas is blown toward the molded substrate at the time of releasing the mold to promote the mold release. The sprue bush 22 is connected to the molding machine nozzle 5 that allows molten resin to flow into the mold. During the molding operation, the stamper 3 is placed on the inner surface of the fixed mold 1a, that is, the surface facing the movable mold 1b, and by the inner peripheral stamper presser 4 and the outer peripheral stamper presser 24 of the fixed mold 1a. Fixed. Movable mold 1
The gate cut punch 7 is provided along the center axis 30 of the b.
Also, the substrate protruding sleeve 6 is mounted on the outer periphery thereof. A cylindrical cylinder 9 is provided on the coaxial outer periphery of the substrate protruding sleeve 6, one end of which is open to the fixed mold 1a side, and the other end has an enlarged cylinder radius. The hydraulic chamber 25 is configured.
A cylindrical piston 8 for compressing an inner peripheral portion that slides in the cylinder 9 is inserted into the cylindrical cylinder 9, and the piston 8 is moved by the hydraulic pressure in the hydraulic chamber 25 in the direction of the fixed mold 1a (in the figure). Only the inner peripheral portion of the molded substrate (resin) can be compressed by moving to the arrow). The outer peripheral portion of the end surface of the piston 8 on the fixed mold 1a side is tapered, and in a non-compressed state, a concave portion 31 is defined in the central portion of the compression surface of the movable mold 1b. The concave portion 31 forms a thick portion on the inner peripheral side of the information recording area of the substrate after molding.

A molding method using an injection molding machine using the mold 1 will be described. First, the fixed mold 1a and the movable mold 1b are clamped by a mold clamping mechanism (not shown) of a molding machine, and then a molten resin such as PC (polycarbonate) or PMMA (polymethylmethacrylate) is moved from the molding machine nozzle 5 to a movable mold. It is injected into the space formed by the die 1b, the stamper 3, and the outer peripheral presser 24. After the space is filled with the resin, the pressure is maintained for a certain period of time in order to supplement the volume contraction of the resin due to cooling. Next, the gate cut punch 7 is projected toward the fixed mold 1a, and the spool portion 26
And the disk substrate 2 are separated. After this, the disk substrate 2
In this case, the hydraulic chamber 25 of the cylinder 9 is cooled.
By adjusting the hydraulic pressure of No. 2 and projecting the compression piston 8 in the direction of the arrow in the drawing, the thick portion on the inner periphery of the information recording area of the disk substrate 2 is compressed. The pressure applied to the compression piston 8 can be controlled according to the change in viscosity when the resin is cooled, and is generally in the range of 5 to 30 MPa. By compressing the thick inner peripheral portion, it is possible to prevent sink defects that occur during the disk substrate cooling process. An appropriate amount of protrusion of the compression piston 8 is the depth corresponding to the depth of the concave shrinkage mark, which is a poor sink mark, and is generally about 0.05 to 0.2 mm. After cooling the disk substrate 2, the compression force of the compression piston 8 is released, the mold is opened, and the disk substrate 2 is peeled off from the fixed mold 1a. Then, the disk substrate 2 is released from the movable mold 1b by blowing gas and projecting the substrate projecting sleeve 6.

In the above example, the movable mold 1b is provided with the mechanism for compressing the thick portion on the inner peripheral surface of the substrate, but it may be provided on the fixed mold 1a side. Further, in the above-described aspect, the compression piston 8 for compressing the thick inner peripheral wall portion of the substrate is provided in the mold, but the compression piston 8 may be provided on the injection molding machine side to penetrate the mold. Further, in the above aspect, only the compression mechanism of the thick inner peripheral portion is shown, but a mechanism for compressing the information recording area may be provided separately from this.
Further, the piston is not limited to being hydraulically driven, but may be pneumatically or mechanically driven.

[0014]

With the mold of the present invention, it is possible to easily prevent sink marks from occurring in the thick inner peripheral portion of the optical recording medium substrate.
Therefore, the molding conditions such as the injection holding pressure, the injection holding pressure time, the mold temperature, and the resin temperature are not limited to the sink defect prevention and can be set in a wide range. Therefore, it is possible to mold the substrate for an optical recording medium which has a small birefringence of the substrate and has no sink defect in the thick portion of the inner circumference.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an injection molding die for an optical disc substrate according to the present invention.

FIG. 2 is a schematic cross-sectional view of a conventional optical disk substrate injection molding die.

[Explanation of symbols]

 1a, 11a Fixed mold 1b, 11b Movable mold 2 Disc substrate 3 Stamper 4 Inner peripheral stamper retainer 5 Nozzle 6 Substrate ejection sleeve 7 Gate cut punch 8 Compression sleeve 9 Compression cylinder 24 Outer peripheral stamper retainer 25 Hydraulic chamber

Front page continuation (72) Inventor Norio Ota 1-88, Torora, Ibaraki-shi, Osaka Prefecture Hitachi Maxel Co., Ltd. (72) Masaki Yoshii, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture Hitachi Production Engineering Laboratory (72) Inventor Hiroki Kuramoto 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Ltd. Production Engineering Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] 1. An optical recording medium comprising a fixed mold and a movable mold, wherein the plate thickness on the inner peripheral side of the information recording region is thicker than the plate thickness of the information recording region and the plate thickness of the information recording region is constant. A mold for injection-molding a substrate from a resin material includes means for compressing only a resin material portion forming an inner peripheral side of the information recording area of the substrate in the fixed mold or the movable mold. A mold for molding a substrate of an optical recording medium, which is characterized in that: 2. The means for compressing only the resin material portion forming the inner peripheral side of the information recording area of the substrate is a piston and cylinder mechanism, and the compression surface of the piston contacts the resin material portion. The mold for molding a substrate of an optical recording medium according to claim 1, which constitutes a part of a compression surface of the fixed mold or the movable mold. 3. A molding machine including the mold according to claim 1.